This invention relates to a method for manufacturing, in high yields, poly-fatty acids mainly in the form of a dimer or trimer or maleic anhydride-added fatty acids from a higher unsaturated fatty acid. Dimers and trimers of higher fatty acids such as, for example, linoleic acid and linolenic acid remain unfrozen even at low temperatures and retain high degrees of viscosity and, therefore, find utility in the production of paints, surface active agents, rustproofing oil additives, lubricating additives, synthetic high polymers, etc. For the manufacture of these polymers, there have been suggested various methods which effect the relevant polymerization reactions by use of a clay catalyst (U.S. Pat. No. 2,347,562), a lithium-containing clay catalyst (Japanese Patent Publication No. 8427/1965, U.S. application Ser. No. 205,099, filed June 25, 1962 now abandoned), a clay catalyst stabilized with a lithium compound (Japanese Patent Publication No. 7477/1967, U.S. application Ser. No. 343,,894, filed Feb. 10, 1964 now abandoned), a synthetic lithium silicate-magnesium catalyst (Japanese Patent Publication No. 980/1966, U.S. application Ser. No. 367,902, filed May 14, 1964 now U.S. Pat. No. 3,405,150 ), an activated terra alba or terra alba catalyst (Japanese Patent Publication No. 5130/1963) and other similar catalysts.
All the methods disclosed to date invariably involve batchwise operations in which unsaturated fatty acids as the raw material are thermally polymerized within pressurized closed vessels for from one to ten hours at temperatures in the range of from 180 to 300.degree. C. in the presence of 5 to 35%, based on said fatty acids, of catalysts. For these polymerization reactions, it is plain that use of a continuous operation is advantageous over that of a batchwise operation. Notwithstanding this fact, no effective continuous process has ever been proposed.
For use as coating compositions, products of addition of maleic anhydride to higher unsaturated fatty acids or to the esters of said acids have been known to excel in hydrophilicity, exhibit high penetrating power, adhere quickly to said substrate as wood and metals and, on desiccation, provide high coating strength, outstanding water resistance and durability (U.S. Pat. Nos. 2,188,882, 2,188,883 and 2,188,890). Besides, as resinous compositions, they are used in lacquers and varnishes to serve the purpose of improving the properties of lacquers and varnishes (British Patent No. 500,348); they have also been demonstrated to serve as excellent base oils for water-soluble paints and to be usable as sizing agents for paper (British Patents No. 500,349 and 500,350); and they serve as excellent rubber compositions and are known to find utility as dispersants for plastics (British Patent No. 500,351). As regards the manufacture of products of addition of maleic anhydride to higher unsaturated fatty acids or to the esters of said acids heretofore known, there have been suggested various methods which accomplish the addition by placing mixtures of higher unsaturated fatty acids or esters thereof with maleic anhydride in closed vessels kept under an increased pressure or normal pressure and heating the charges in the absence of a catalyst for a period of from one to ten hours at temperatures in the range of from 150 to 300.degree. C. (U.S. Pat. Nos. 2,188,882, 2,188,883 and 2,188,890 and British Patent No. 500,348, 500,349, 500,350 and 500,351). It has recently been established that activated terra alba accelerates the reaction of addition of maleic anhydride to linoleic acid and at the same time inhibits a secondary reaction (J. of Japan Oil Chemists Society, 24, 149(1975)). All the methods heretofore suggested for the addition reaction invariably cause the reaction to be carried out batchwise, namely, by use of fixed vessels. It is only evident that for the purpose of such an addition reaction, use of a continuous operation proves to be advantageous over that of a batchwise operation. Notwithstanding this fact, no effective continuous process has ever been proposed.
An object of the present invention is to provide a method for manufacturing poly-fatty acids mainly in the form of dimers and trimers by continuously polymerizing fatty acids under normal pressure.
Another object of the present invention is to provide a method for continuously manufacturing maleic anhydride-added fatty acids.